1. Field Of The Invention
The present invention relates to a valve for controlling fluids and more particularly to such a valve including a piezoelectric actuator disposed in an actuator bore.
2. Brief Description Of The Prior Art
FIG. 2 shows a valve for controlling fluids in accordance with the prior art. The valve 1 includes a housing 4, in which there is an actuator bore 3 for receiving a piezoelectric actuator 2. The piezoelectric actuator 2 is connected to a hydraulic booster 11 via an actuating piston 15. The hydraulic booster 11 comprises a first piston 12, a second piston 13, and a fluid-filled pressure chamber 14 disposed between the two pistons. For sealing the actuator module off from the hydraulic booster, an O-ring 17 and a metal bellows 5 are provided. The O-ring 17 is disposed in an annular recess in a disk 18 and seals off the actuator module at the actuator bore 3. The metal bellows 5 is connected on one end to the actuating piston 15 and by its other end communicates with an inner bore in the disk 18. As a result, the metal bellows 5 seals off the actuator module in the region of the actuating piston.
In the valve 1 known from the prior art, it is disadvantageous, however, that the O-ring 17 can become damaged at the insertion edge as the valve is being assembled. Also, the O-ring 17 does not seal off the actuator module one hundred percent. Moreover, the tightness furnished by the O-ring cannot be checked. In addition, via the insertion path of the O-ring into the actuator bore, it can happen that the O-ring will twist or turn, which can cause eventual leaks. Because of the relatively limited installation space, the actuator spring can be embodied with only a few windings. The consequence can be that the spring becomes skewed relative to a center axis of the valve, so that the introduction of force to the actuator takes place eccentrically. This can cause rapid wear of the valve.
The valve for controlling fluids according to the invention has the advantage over the prior art that it no longer requires an O-ring for sealing purposes. Sealing off the actuator module from the hydraulic booster is achieved such that a bellows is solidly connected to the actuator and to the actuator bore. As a result of this feature of the invention, both the O-ring and the disk in which the groove for the O-ring is provided can be dispensed with. This reduces the number of component parts, and the valve of the invention can be produced more simply and economically. With the elimination of the disk, still more installation space is gained, or in other words the valve of the invention can be constructed more compactly. Especially If the valve is used as an injection valve for an engine, this is a major advantage, since the space available in the engine compartment is limited, and hence the valve can be installed in different engines from the most various manufacturers without requiring modifications.
To enable simple assembly and to furnish the most variable possible installation of the bellows in the valve, the bellows preferably has a sleevelike extension that can be solidly connected to the actuator bore. Thus depending on the length of the sleevelike extension, the bellows can be guided directly along the inside of the actuator bore and secured to the actuator bore at an arbitrary point.
To furnish a simple, economical production of the valve of the invention, the connection between the bellows and the piezoelectric actuator and/or the connection between the bellows and the actuator bore is embodied as a welded connection. Especially advantageously, the connection is embodied here as an annular welded connection. This also makes it possible, after the welding operation, to check the tightness between the bellows and the actuator on the one hand and between the bellows and the actuator bore on the other. A long service life of the valve of the invention is thus assured.
In a further advantageous feature of the present invention, the sleevelike extension of the bellows is solidly connected to the actuator bore via a press fit of a retaining body. As a result, the sleevelike extension is disposed between the wall of the actuator bore and the retaining body. The retaining body can also be provided so as to receive the hydraulic booster of the valve at least in part. Because of the annular press fit of the retaining body, a partial deformation of the sleevelike extension of the bellows thus ensues, causing it to rest sealingly from its top to its underside on the actuator bore. At the same time, the retaining body is positioned in the valve thereby. As a result, the welding point between the sleevelike extension of the bellows and the actuator bore can be omitted.
In order to absorb a sufficient axial stroke of the actuator, the bellows preferably has three undulations. However, the number of undulations can be greater or fewer, depending on the required length of the axial stroke.
In order to have an adequate service life, the bellows is preferably produced from metal.
To prevent skewing of the restoring spring for the actuator and an eccentric introduction of force by the spring, the restoring spring preferably has at least four windings. The windings are advantageously designed such that they rest on the actuator bore, but without generating a large amount of friction.